Mucins are heavily glycosylated, high molecular weight glycoproteins with a carbohydrate content of up to 80% that are secreted by seroviscous tissues in the mouth, lungs, cervix and intestines. Mucins have been identified as tumor-associated antigens and have been isolated from the serum and ascites fluid of cancer patients, including those with breast cancer.
The fat globules of human milk are contained in a particular membrane derived from the plasma membrane of the apical surfaces of lactating cells. Interest in this membrane, known as the milk fat globule membrane (hereafter MFGM), has increased with the demonstration that some of the antigens found within the MFGM are mucin-like and are tumor-associated, particularly with carcinomas of the breast. Antibodies directed to epitopes on mucin antigens associated with breast cancer have been obtained from mice immunized with fragments of human milk fat globule (HMFG). These antibodies show promise for the diagnosis of breast tumors. Of particular interest are antibodies directed against high molecular weight (Mr greater than 200,000) mucin-like components of the MFGM. Antibodies to mucin-like antigens have been used successfully to diagnose micro-metastases in biopsies, as an indicator of tumor prognosis for radio-localization of tumors, and for serum assays to monitor tumor progression. Linsley et al., Cancer Research, 46, p. 5444-5450, (1986), incorporated by reference herein.
Most of the mucin antigens previously characterized have been found to be present in normal tissues in addition to tumor tissue. Variations in mucin-like antigens from normal and tumor sources have been studied by Burchell et al., J. Immunol., 131, p. 508 (1983), who found differences in the ratios of determinants recognized by two monoclonal antibodies (HMFG-1) and (HMFG-2) in normal human breast epithelial cells and in breast tumor cell lines. These investigators showed that the relative levels of binding of HMFG-1 and HMFG-2 varied between cell lines from normal and malignant breast epithelium, with the HMFG-2 epitope being more strongly expressed on the tumor cell lines. Sekine et al., in J. Immunol., 135, p. 3610 (1985), compared mucin-like antigens reactive with the DF3 monoclonal antibody, Kufe et al., Hybridoma, 3, p. 223 (1984), from milk and pleural effusion fluids from breast cancer patients. These studies suggest that mucins are antigenically complex, expressing a variety of epitopes on both normal and tumor tissues, and also indicate that mucins may vary in the expression of epitopes between different tissue sources. Antibodies that react with epitopes on mucin-like antigens that are found at elevated levels in sera from breast cancer patients, have also been described (Linsley et al., supra, and Frankel et al., J. Biol. Response Modifiers, 4, p. 273 (1985)). One of these antibodies, W1, is reactive with epitopes on a mucin antigen associated with breast cancer cells. W1 antibody has been used in an assay to detect the presence of antigen at elevated levels in serum from breast cancer patients (Linsley et al., supra). In addition to the W1 epitope, other epitopes, such as the T (Thomsen-Friedenreich) and Tn mucin epitopes which have been known to be associated with carcinomas, may be detected in an assay using monoclonal antibodies. Springer and Desai, Molecular Immunology, 22, pp. 1303-1310 (1985); and Springer, Science 224, pp. 1198-1206 (1984).
It would be desirable to develop new antibodies which demonstrate increased specificity in assays for tumor-associated antigens present in samples from human subjects. Optimally, such antibodies should be capable of identifying specific epitopes on a tumor-associated mucin antigen, which epitopes are found at greatly reduced levels on, or are masked on antigen derived from normal tissues. Such antibodies could then be used to perform more sensitive assays for detecting the presence of cancer by preferentially reacting with tumor-associated antigens in sera from patients with cancer.